1. Field of the Invention
The present invention relates to a process for the preparation of a nickel-cobalt hydroxy carbonate product, particularly to the preparation of an encapsulated nickel hydroxide or basic nickel carbonate compound suitable for use as battery chemicals. In particular, the present invention relates to a process for the preparation of cobalt oxide hydroxide (CoOOH) coated nickel hydroxide or basic nickel carbonate particles. The basic nickel carbonate may have the typical structure [NiCO3.2Ni(OH)2.4H2O], however particles having other carbonate/hydroxy ratios may be present.
The invention also relates to a nickel-cobalt hydroxy carbonate product, particularly to a coated nickel hydroxide or basic nickel carbonate product, produced by the process of the invention described herein.
The nickel-cobalt hydroxy carbonate product of the invention may be used as:                (a) an active material of a non sintered type positive electrode for alkaline storage batteries, or        (b) a component, when blended with lithium hydroxide and calcined, of lithium secondary batteries.        
The increasing popularity of battery powered portable equipment requires batteries with increased capacity which in turn can be met by improving the utilization of nickel hydroxide used as an active material in the positive paste electrode.
2. Description of Related Art
With reference to (a) above, the prior art associated with the preparation of active material for alkaline batteries is reviewed.
It has been reported that coating the surface of nickel hydroxide particles with cobalt hydroxide is an effective way of achieving electrical conductivity between nickel hydroxide particles thus improving their utilization and consequently battery performance.
In U.S. Pat. No. 6,040,007, this end result of cobalt hydroxide coated nickel hydroxide particles is achieved in a two stage process where nickel hydroxide particles formed in one reactor are then transferred to a second reactor where cobalt hydroxide solids are precipitated onto the surface of the nickel hydroxide particles. The conversions of the cobalt hydroxide (cobalt II) to cobalt oxyhydroxide (cobalt II) can be done by post precipitation oxidation using electrochemical or chemical means such as persulphates and hypochlorites.
In European patent EP 0851516 A2, nickel hydroxide particles were prepared by the addition of aqueous sodium hydroxide to a nickel sulphate solution under controlled conditions to produce nickel hydroxide solids which were then coated with cobalt oxide hydroxide previously prepared by the dry oxidation of cobalt hydroxide solids at temperature. Again what is described is a two step process at least to achieve a cobalt encapsulation of nickel hydroxide with a higher valence cobalt oxide.
In U.S. Pat. No. 3,928,068, a process is described for the production of an electrode paste composed of the higher valence states of both Ni and Co. This material is prepared by adjusting the pH of an aqueous slurry of basic nickel carbonate and dissolved cobalt nitrate to precipitate cobalt hydroxide onto the basic nickel carbonate particles followed by hypochlorite oxidation of the resultant slurry.
This again is at least a two stage process prior to the oxidation step as the basic nickel carbonate solids have to be prepared initially. This latter step is not described in the patent.
European patent EPO 727834 A1 discloses the preparation of an active material for a non sintered electrode for use in alkaline storage cells comprising a solid solution of nickel hydroxide mixed with manganese and also incorporating other elements such as cobalt. The solids described in this patent were coprecipitated from aqueous solution by the addition of sodium hydroxide at controlled pH of 11. In this patent, no mention of utilization enhancement by encapsulation of the solid solution by cobalt hydroxide precipitation is made nor of the oxidation of the cobalt II compounds to a higher valence state.
European patent WO96/14666 describes the encapsulation of nickel hydroxide particles with cobalt hydroxide in a two step process where the aqueous slurry of nickel hydroxide solids is stirred vigorously with a cobalt sulphate solution during the addition of potassium hydroxide to pH 8. The encapsulating layer of cobalt hydroxide was then able to be oxidized electrochemically or by air oxidation immediately following precipitation.
With reference to (b) above some prior art descriptions are reviewed.
Patent EP0720247 A1 describes the preparation of composite hydroxides of nickel and cobalt by coprecipitation on the addition of caustic alkali to aqueous solutions containing cobalt and nickel salts. The composite hydroxides, when mixed with lithium hydroxide and heated to 750° C. form a single phase most suitable for positive electrodes in lithium secondary batteries.
Patent WO98/05592 describes the preparation of a nickel cobalt hydroxide composite precipitate by the addition of a base to an aqueous solution of nickel and cobalt sulfates at controlled pH of 10.5. When the composite hydroxide is blended with lithium hydroxide and calcined it forms a single phase lithium nickel cobalt dioxide suitable for lithium secondary batteries. The inventor also describes the use of cobalt III oxide (CO2O3) blended with nickel hydroxide and lithium hydroxide and calcined in the presence of potassium hydroxide.
It is apparent from the above prior art that the production of an active material for non sintered electrodes is only achieved by a series of consecutive steps.
The above discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.